Prior to the present invention, nylon compositions were prepared by anionic polymerization of a lactam in the presence of an anionic polymerization catalyst and a promoter such as an isocyanate or N-acyllactam compound. A typical nylon polymerization procedure is shown by Mottus et al., U.S. Pat. No. 3,017,391. Although the nylon compositions of Mottus et al. provide useful materials, the polyamide compositions require the use of an anionic polymerization catalyst, such as sodium hydride which must be protected from atmospheric moisture. In certain instances, moisture-sensitive catalysts are not required for lactam polymerization. However, in such cases the reaction is often slower and higher temperatures are needed for a satisfactory polymerization rate.
In copending application Ser. No. 706,374, anionic polymerization of lactams was achieved by using certain lactam polymerization promoters having silicon attached to the lactam nitrogen by silicon-nitrogen linkages. Base catalyzed crosslinkable blends of lactam and silicon substituted lactam, convertible to high molecular weight polyamide, were obtained upon heating. In addition, reinforced crosslinked polyamide was obtained by incorporating into such silicon-lactam blends, high performance aromatic thermoplastic polymers, or inert materials, such as glass fiber or reinforcing silica.
The present invention is based on my discovery of a substantially moisture insensitive catalyst for lactam polymerization. The catalyst is a fluoride ion which is used in combination with a promoter, such as an isocyanate, and a certain silicon containing material, for example, an N-silylated lactam or alkoxysilane. Advantageously, the catalyst, in addition to being substantially moisture insensitive, is capable of effecting lactam polymerization at temperatures as low as 25.degree. C.